An optical fiber sensor has been invented that sensitively detects temperature changes, particularly cryogenic temperature changes. Specifically, the invention is a specially-designed temperature sensor that utilizes a fiber grating in conjunction with an integrated, localized fiber coating to measure temperatures as low as about ten Kelvin (10 K), or below.
Silica, of which optical fibers are often constructed, predictably expands and contracts when exposed to temperature changes. Fiber optic sensors have been fabricated that take advantage of this predictable behavior, as well as the foreseeable results of thermally-induced optical changes in silica, in order to transduce changes in temperature into meaningful signals. However, silica fibers have a very small, almost negligible, thermal expansion coefficient ("TEC") below about one hundred and fifty Kelvin (150 K). Because thermal expansion and contraction is the primary mechanism for inducing signal changes in fiber optic thermo-transducers, traditionally-crafted optical fiber Bragg grating ("FBG") temperature sensors inherently lack sensitivity, and thus their ability to be useful in broad temperature ranges is impaired, particularly at cryogenic temperatures.
In the past, fiber grating transducers have been used for sensing applications in which temperature changes occur along with a change in some other physical phenomena, such as strain. In these applications, however, a signal alteration caused by a temperature change is indistinguishable from an alteration caused by some other physical phenomena. This lack of discernment limits the utility of such devices.
As a result, there is a need for a fiber optic transducer that allows temperature-referenced measurement of physical phenomena. Additionally, there is a need for an invention that allows sensitive measurement of low temperature in the presence of strong electromagnetic fields and in explosive environments. Additionally, there is a need for an invention that allows detection of low temperature changes, as well as temperature changes across a distributed area. Moreover, there is a need for an optical fiber invention for cryogenic temperature measurement that is very accurate, easy to calibrate and use, and allows the fiber to remain flexible.